Both Garmin and TT have always been very late in adding urban new developments. I still suspect they don't get the info from the various agencies as frequently as they make out.
They can also get it wrong the other way round. The Hindhead tunnel appeared on some SatNavs before it was opened.
I did submit a new housing development in Great Malvern to Garmin, back in the 90's, and they did have it mapped 2 updates later.